Vacuum arc devices with ferrous electrodes

ABSTRACT

Vacuum arc devices having a pair of primary arc-electrode assemblies in the form of a rod array structure utilize hardened ferrous materials exhibiting high hardness, ductility and high recovery strength for the attainment of higher voltage handling capacity and higher current interrupting characteristics than devices utilizing conventional nonferrous cuprous alloy electrode materials.

[ Oct. 30, 1973 6/1965 Hoeh 313/311 X 4/1926 Brach...... 3l3/3ll XABSTRACT 19 Claims, 5 Drawing Figures United States Patent [1 1 HarrisVACUUM ARC DEVICES WITH FERROUS 3,189,777 1,532,330

ELECTRODES [75] Inventor: Lawson P. Harris, Scotia, N.Y.

[73] Assignee: General Electric Company,

Primary Examiner-John Corbin Attorney-John F. Ahern et al.

[22] Filed:

Vacuum are devices having a pair of primary arc- [21] Appl. No.: 236,278

[52] US. 313/233, 200/144 B, 313/267,

electrode assemblies in the form of a rod array struc- 313,311 tureutilize hardened ferrous materials exhibiting high hardness, ductilityand high recovery strength for the 7 Q6 12 s 4 2 3 3 3/ 3 1 3 1. m m mhc r a e S m l d Ld mm 1] 8 55 attainment of higher voltage handlingcapacity and higher current interrupting characteristics than devicesutilizing conventional nonferrous cuprous alloy electrode materials.

[56] References Cited UNITED STATES PATENTS PATENTEU EU 30 L973 SHEET 1BF 3 PATENIEUHU 3 0 I975 13,769,538 SHEET 20F 3 PATENTEU 001 3 0 I973SHEET 3 BF 3 BACKGROUND OF THE INVENTION The present invention relatesto improved vacuum are devices. More particularly, the invention relatesto such improved devices as vacuum gaps, triggerable vacuum gaps, vacuumswitches and the like, wherein a rod array structure of interleavedindividual arc electrode members presents a large arcing surface for theattainment of high current and low current density power arcingcharacteristics. In the development of vacuum arc devices such as vacuumgaps and vacuum switches, a number of problems have been encountered andsolved. One of the most recent problems solved is that of the formationof anode spots due to the bunching of arc current conduction pathsbetween the cathode and anode assemblies in structures wherein aplurality of interleaved electrode members is utilized in order toattain a large area of arcing surface in order to maintain a low arccurrent density. In many prior art devices, the configuration of suchelectrodes caused inter-electrode arcing currents and the magneticfields caused by conduction of current in electrode members to interactso that the resultant TX B forces caused the formation of bunching ofcurrent paths and the formation of destructive anode spots. Recently, asis set forth in application Ser. No. l07, 51 I, filed Jan. 18, 1971, nowU.S. Pat. No. 3,679,474, Joseph A. Rich assigned to the present assigneeand incorporated herein by reference thereto, thisproblem has largelybeen overcome by the provision of electrode assemblies each comprisingopposed rod arrays of individual arcing electrode members which aredisposed in a circular pattern normal to an arc-electrode plate to whichthey are electrically and mechanically affixed, and juxtaposed withrespect to an oppositely poled arc-electrode assembly of likeconfiguration so that the individual rods of opposite arc-electrodeassemblies interleave between one another to cause a plurality of arcingpaths electrically in parallel. This arrangement has resulted in asubstan; tial cancellation of all but residual azimuthal J X B forces,with the resultant substantial elimination of bunching of arcing pathsat the anode electrode and the formation of destructive anode spots.

While devices of the Rich invention are a great advance upon the art andmake possible the attainment of heretofore unobtainablecurrent-interrupting and current-carrying capacities without theformation of anode spots, the utilization of conventional arcelectrodematerials as, for example, zone-refined OFHC copper, does not over-comethe disadvantage existing in previous vacuum arc devices wherein suchmaterials do not exhibit a high enough recovery strength nor dielectrichold-ofi' strength to accommodate higher voltages and further possesscertain limitations in physical strength which limit thecurrentinterrupting capacities.

Accordingly, it is an object of the present invention to provide vacuumare devices wherein the advantage of previous structures which avoidanode spot formation is utilized and wherein higher dielectric anddielectric-recovery strength is obtainable.

Still another object of the present invention is to pro vide such vacuumarc devices as possess improved mechanical strength which facilitatesthe attainment of higher current interruption than devices of the priorart.

Yet another object of the present invention is to provide improvedvacuum are devices suitable for holding off higher voltages,interrupting higher currents, operating with better electricalcharacteristics than devices of the prior art and which are fabricatedfrom inexpensive materials which do not require expensive fabricationprocesses.

BRIEF DESCRIPTION OF THE INVENTION Briefly stated, in accord with oneembodiment of the present invention, vacumm are devices in accord withthe invention include a pair of primary arc electrode assemblies each ofwhich comprises a base plate and a plurality of rod-like arcing membersnormal thereto formed in a substantially circular pattern and adapted,so that when a pair of oppositely-poled assemblies are interleaved withone another, a plurality of electrically parallel arcing paths areformed. In further accord with the present invention, such arc electrodeassemblies are fabricated of a gas-free hardened ferrous material whichexhibits a high hardness and ductility and a higher dielectric strengththan materials previously utilized in such applications.

The novel features characteristic of the present invention are set forthin the appended claims. The invention itself together with furtherobjects and advantages thereof may best be understood by reference tothe following detailed description taken in connection with the appendeddrawing in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic verticalcross-sectional view constructed in accord with the present invention.

FIG. 2 is a plan view taken along the lines 22 of the device of FIG. 1.

FIG. 3 is a graphical representation of the voltage recoverycharacterics of arc electrodes in vacuum fabricated of materialsutilized in the construction of devices in accord with the presentinvention as compared with the similar characteristics of arc-electrodesfabricated of materials normally used in vacuum arc devices.

FIG. 4 is a schematic vertical cross-sectional view of a triggerablevacuum gap device constructed in accord with the present invention, and

FIG. 5 is a schematic vertical cross-sectional view of a vacuum switchconstructed in accord with the present invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, a vacuum gap deviceconstructed in accord with the present invention is representedgenerally at 10. Device 10 includes an upper arc-electrode assembly 11and a lower arc-electrode assembly 12 which are joined by an insulatingcylindrical sidewall member 13 hermetically sealed to upper and lowerelectrode assemblies 11 and 12 to form an hermetically-sealed evacuableenvelope 14. Upper arc-electrode assembly 11 includes a base plate ordisk member 15 and a plurality of downwardly-depending electrode members16 electrically and mechanically attached thereto. Lower electrodeassembly 12 includes a base plate or disk member 17 and a plurality ofupwardly-depending electrode members 18 electrically and mechanicallyattached thereto and disposed in perpendicular relationship therewith,as are the electrode members 16 with respect to baseplate member 15. i

Each of electrode members 16 and 18 are solid, smooth-surfaced rod-likemembers, as illustrated. Although a cylindrical geometry is believedideal, it is within contemplation of the invention that roundedwedge-shaped or radial vanes with no sharp edges may also be used forattainment of increased arcing area.

The interleaving of arc-electrode assemblies of 11 and 12 into oneanother results in the creation of a plurality of parallelinterelectrode gaps illustrated at 21 in FIG. 2 of the drawing whereinthe arc-electrodes of one polarity are indicated with a singleperipheral line and the electrode members of the opposite polarity areindicated with a double peripheral line.

Envelope 14 is completed and seals are made by the provision ofconventional ceramic-to-metal seals by collar-shaped seal members 22 and23 which seal upper electrode and lower electrode assemblies toinsulating sidewall member 13, respectively. These seals are protectedfrom the deleterious effects of being exposed to an electron-ion plasmacaused during intense arcing conditions within envelope 14 by theprovision of end shields 24 and 25 connected to stepped peripheralportions of endwall members and 17, respectively. The insulatingintegrity of insulating sidewall member 13 which may for example be aglasssuch as General Electric REX or Corning Pyroceram or a higherdensity alumina or any of the many vacuum tight glasses well known tothe art, is further protected by a doubly truncated cylindrical centralshield member 26 which is supported laterally about the region in whicharc electrode members 16 and 18 overlap and which overlaps theinwardly-depending ends of end shields 24 and 25. Shield 26 is supportedby shield support member 27 which is secured in ceramic-to-metal bondwithin the central portion of insulating sidewall member 13. A pair ofterminal members 28 and 29 comprise means for connecting the device 10of FIG. 1 in circuit with an electric circuit or circuit element to beprotected. Such relationship may be in series circuit relationship withan inductive load member for example or in parallel circuit relationshipwith a capacitive load member for example. Terminal members 28 and 29are in good nonresistive electrical contact with arc electrodeassemblies l1 and 12, respectively, and are adapted to conduct hundredsof kiloamperes.

In the pertinent history of the development of vacuum are devices,development has been directed along the line of providing materials ofintermediate vapor pressure to provide arc conduction specie for suchdevices and which, additionally, may readily be vacuum processed toremove therefrom all sorbed gases or gasforming constituents which, uponthe formation of a high current arc can cause the evolution of gaseouscontaminants which would permanently affect the maintenance of a steadystate equilibrium vacuum of the order of 10 torr. A furtherconsideration has been the seeking of arcing materials which exhibitgood chopping" characteristics, namely, the ability to hold a current asa cycle of a current alternation upon which an arc has been struckapproaches zero without having the current chop and abruptly fall from arelatively high value to zero, with the creation of high transientvoltages which can be highly detrimental to inductive loads for example.FOr these reasons, among others, the art has concentrated upon the useof copper and cuprous alloys in vacuum arc devices. Furthermore, therehas been an unwritten folklore that the use of any ferromagneticmaterials in arcing electrodes in vacuum are devices would result inunpredictable and deleterious electromagnetic effects and is, therefore,to be avoided. For this reason, innovators working with arcing materialshave generally avoided ferrous materials.

In accord with my invention, however, I find that ferrous materialsprovide unique advantages in the state of the art to which it hasdeveloped for the attainment of very high current interruption and themaintenance of high dielectric strength. I further find that, so long asferrous materials are not utilized for steady-state conduction of highcurrents that their use in the sustenance of kiloampere arcs and arcingcurrents for the order of one cycle of power frequency alternatingcurrent does not provide any problem, even considering the much higherresistivity of ferrous materials than cuprous materials. This is true atthis time because present vacuum arc device technology has overcomeearly (e.g. 19501960) problems relating to maintenance of sufficientarcing specie to sustain an arc, avoiding unacceptable choppingcurrents, and avoiding the formation of destructive arc footpoint spots,particularly anode spots. The present problems facing innovators in thevacuum arc device relate largely to extending the magnitude of voltagewhichmay be safely impressed between arcing members and increasing thecurrents which may be interrupted and terminated thereby.

Since the chopping characteristic of iron and of ferrous materials ingeneral is compatible with vacuum are use, and so long as ferrousmaterials are not used for steady-state conduction, there is noelectrical disadvantage to their proper use in vacuum arc devices. Ifind, however, there are decided advantages. Thus, for example, thedegassification of ferrous matierals is relatively simple. Initialdegassification of the bulk material may be provided by vacuum melting,particularly of the consumable electrode type vacuum melting whereineach portion of a ferrous bar from which the finally utilized ferrouselectrode is formed is at one point the arcing point of a vacuum arc andeach portion of the arc electrode source material is melting undervacuum conditions to cause the removal of all gas and gasformingconstituents before formation of the electrode. Once the electrodes havebeen formed from such material, the problem of surface degassificationis much simpler than that with cuprous materials which have relativelylow softening and melting points. Ferrous materials may be degassifiedof adsorbed gases merely by assembling them in the vacuum arc device andduring normal bakeout subjecting them to the temperature and time ofbakeout necessary to degassify the other materials in the device. Nospecial precautions need to be taken.

when one considers the structure as is set forth in FIG. 1 of thedrawing and considers the electromagnetic forces which may be applied toeach individual rod electrode upon the passage of a current of the orderof hundreds of kiloamperes through the device, it is apparent that greatstress is placed upon each individual rod. I find that utilizing ferrousmateriala, particularly hardenable steels which have high ductility,rather than cuprous materials precludes deformation of the rods forcurrents which materials, attainable within the limitations of otherparameters of such devices so that possible deformation of individualrods vanishes as a problem, thus creating another advantage for the useof ferrous materials. Finally, and perhaps of greatest importance,ferrous metals as used in accord with the invention are usually veryhard and reasonably ductible. I have found that such hardness andductility is associated with high dielectric recovery characteristicsand high electrical breakdown strength, thereby greatly facilitating asubstantial increase in voltage rating of devices in accord with theinvention as compared with prior art devices utilizing conventionalelectrode materials. This advantage is in addition to the mechanicaladvantage gained by the use of hard, ductile electrodes. While numerousferrous materials are useful in the production of vacuum arc devices inaccord with the present invention, I find that certain hardenable steelshaving martensitic grain structure and certain precipitated inclusionsare particularly useful. Many of these steels may be machined whilerelatively soft in condition and then heat-treated to cause an increasein hardness and yield strength and are ideally suited for devices inaccord with the present invention. One general grouping of such steelsis well known and generally identified as age hardening or precipitationhardening steels. In general, these steels are martensitic steelsobtained by quenching rapidly an austenitic steel to obtain dispersionof impurities and small grain size. Hardening is effectuated by thepresence of impurities, which also contribute to the necessaryductility. The hardening may result from a heat treatment generallyperformed at a relatively low temperature (as compared with thetemperature of the original quenching), as for example between 900-1000F. Some such steels are iron-nickel maraging steels (generallycontaining also minor quantities of molybdenum and cobalt, and sometimestitanium) with from 15 to 30 weight percent nickel. Some such steels aredescribed in an article entitled 18% Nickel Maraging Steel by Decker,Eash and Goldman, published in the Transactions of the ASM, pp. 58-76,1962. Certain specific maraging steels which have been found suitablefor use in the invention are available from Vanadium Alloy Steel Co.,Latrobe, Pennsylvania, and are described in a brochure copyrighted bythat firm in 1966 entitled VASCOMAX 200-250-300-350 which brochure listsmany specific compositions of suitable steels.

Maraging steels are often manufactured by vacuummelting practices andare relatively free of dissolved gases as commercial steels go.Developmental tests have verified that the gas contents of these steelsis acceptable for use in arc electrodes in vacuum are devices. Aspurchased commercially, maraging steels may typically have a hardness ofapproximately 30 Rockwell C and exhibit a yield strength ofapproximately 100,000 psi, approximately six times that of copper. Inthis condition the steels are, nevertheless, readily machinable, muchmore so than copper. After machining, forming and other preparation forassembly into the devices of the invention, the maraging steels may behardened by a high-temperature aging treatment, the temperature and timeof which may be varied compatibly to achieve the useful result. Thus,for example, a typical 30 Rockwell C 100,000 psi maraging steel, aftertreatment at 520 C for approximately three hours, exhibits a hardness of54 Rockwell C and a yield strength in excess of 250,000 psi withremarkably high ductility in excess of percent of 2 inch standardsection. Such characteristics are uniquely adapted for the formation ofelectrode assemblies in vacuum arc devices since the bakeout and curingtime of such devices may be made sufficient to cause appropriatehardening of a marging steel.'i"hus, for example, I have constructedvacuum devices in accord with the present invention utilizing aparticular maraging steel known as Vascomax 300 CVM to formarc-electrode members exhibiting the foregoing mechanicalcharacteristics. A similar Vascomax 300 CVM maraging steel having a 30Rockwell C hardness was machined to provide base plates 15, 17 and rods16, 18 of vacuum arc electrode assemblies in accord with the presentinvention, assembled, and the device was baked out for 24 hours at 550C.After such treatment, the steel was found to exhibit a hardness ofapproximately 41 Rockwell C and a corresponding yield strength of150,000 psi, at least ten times stronger than conventional vacuumprocessed OFHC copper, generally utilized in such devices and aductility in excess of 10 percent. As is mentioned hereinbefore, forshort term arcing characteristics, the steels of the invention arecomparable to copper insofar as arcing current-carrying capacity isconcerned. Developmental tests of Vascomax 300 steel utilized asdescribed herein have shown an ability to carry without deleteriouseffect a current density of approximately 225 amperes/cm over thesurface thereof for a half cycle of arcing, which exceeds the same valueas may be carried by copper electrodes.

Other hardened or hardenable steels from which ferrous arc-electrodesfor use in devices in accord with the invention are made, includeprecipitation hardened stainless steel such as those set forth on pages81 and 83 of the 1972 Materials Selector published by MaterialsEngineering Journal, Stamford, Connecticut. Such precipitation-hardenedstainless steels, no one of which is unique in desirable properties asused herein, usually contain low carbon, high nickel and chromium andminor precipitates of other elements. They are generally hard, havingtensile strengths in excess of 150,000 and usually in excess of 200,000psi, are easily outgassed and have ductility of the order of 10 percentelongation of standard 2 inch section. Many other precipitation hardenedstainless, austenitic and martensitic steels may be found therein.

One specific precipitation hardened stainless steel possessingcharacteristics ideally adapted for use in devices in accord with theinvention is identified as Carpenter Custom 455 and is available fromCarpenter Technology Corporation, Reading, Pennsylvania. This steelcontains approximately 12 percent chromium, 8.5 percent nickel, 1.2titanium, 2.25 percent copper, less than 1 percent each of carbon,manganese and columbium, balance iron. Its tensile strength is in excessof 225,000 psi, readily outgassed and has high ductility as representedby a 5-10 percent elongation in a standard 2 inch test section.

Still another class of uniquely adapted hardened fer rous materials oralloys well adapted for use in devices in accord with the invention arethe so-called TRIP steels (Transformation Induced Plasticity). Suchsteels are normally austenitic, but their composition places them nearthe phase line so that warm working causes a transformation tomartensite under stress at service temperatures. A description of TRIPsteels may be found in an article appearing in preprint No. -UCRL 18609(Lawrence Radiation Laboratory), University of California, November1968, by W. W. Gerberich and entitled Metastable Austenitic Steels WithUltrahigh Strength and Toughness." See also TRANS. ASM 60, 252 (l967),The Enhancement of Ductility in High Strength Steels by Zackey et al.

In general, another class of ferrous alloy materials which may beutilized in accord with the present invention is that of carbon alloysteels. These steels differ from maraging steels, and other hardenablesteels which are often softened by quench from a high temperature inexcess of 1500F and hardened by later exposure to intermediatetemperatures of the order of 900F l200F that correspond reasonably wellto bakeout temperatures of vacuum are devices in accord with the presentinvention. Carbon alloy steels, on the other hand, as is epitomized, forexample, by Vascojet 1000 CFM, a carbon alloy steel'available fromVanadium Alloy Steel Co., Latrobe, Pennsylvania, and comprisingapproximately 0.40 percent carbon, 5.0 percent chromium, 3 percentmolybdenum, 0.5 percent vanadium, the remainder iron, are hardened by aquench from a high temperature (l800-l900F for Vascojet) and latertempered to slightly decrease the hardness and increase theductility byexposure to intermediate temperatures such as those utilized in thebakeout of vacuum arc devices in accord with the present invention. 7

The importance of ductility in arc-electrodes of vacuum are devices inaccord with the invention cannot be stressed too heavily. The enormousshocks caused by the electromagnetic forces of kiloampere arcs candeform strong arc electrode structures. If the structures are merelymade hard, they may be brittle, and, when stressed, may crack or break.The advantages 'of the invention are only achieved when the hard ferrousmaterial utilized is sufficiently ductile, as is defined herein,

to withstand the shocks and absorb the same without deforming orshattering.

It is apparent to those skilled in the art that with the opening of thepossibilities of hard, ductile ferrous alloys such as maragingprecipitation hardened steels, TRIP steels, and carbon steels which arecapable of having their crystal structure grain size and othermetallurgical characteristics altered by temperatures of annealing whichmay correspond with acceptable temperatures for the bakeout of vacuumare devices in accord with the present invention, that this inventionmay be practiced with numerous such steels, many of which may providethe increased strength, hardness and ductility which are desirable andconsistent with the attainment of more stable vacuum arc structures forthe attainment of higher current-carrying capabilities and greaterdielectric strength. Accordingly, it is well within the contemplation ofthose skilled in the metallurgical arts to apply the teachings of thepresent invention to the use of an infinity of ferrous alloys for theprovision of improved vacuum arc devices.

As used herein, and in the appended claims, the terms hardness, hard andthe like are intended to connote a tensile strength in excess of 100,000psi and preferably in excess of 150,000 psi. As used herein, the termshigh ductility," ductile and the like are meant to connote a ductilityas evidenced by a percentage elongation of a standard 2 inch long sampleof standard cross section of at least percent and preferably 10 percent.All percentages of compositions are expressed in weight percent.

As is stated hereinbefore, yet another unexpected advantage of devicesin accord with the present invention is the discovery of a uniquedielectric recovery strength characteristic of ferrous arc electrodes ofductile, hardenable steels, when used in accord with the presentinvention. FIG. 3 of the drawing illustrates a typical plot of recoverystrength in volts plotted as a function of time after arcing of gas-freearc-electrodes of a specific configuration utilized in vacuum aredevices of the present invention fabricated from different electrodematerials and tested under identical test conditions. As may be seen,the voltage recovery strength of arc electrodes fabricated from cuprousand ferrous materials increases rapidly at a rate of approximately 15kilovolts per microsecond on a more or less straight line characteristicand saturates at a value which is dependent upon the material of theelectrode and its physical characteristics, principally hardness. As mayreadily be seen from the graph of FIG. 3, the curve representing cuprouselectrodes saturates at 30 kilovolts while the curve representative ofelectrodes of Vascomax 300 maraging steel as an example of hard ferrouselectrodes does not saturate until kilovolts, nearly three times higherthan that for the copper electrodes, thus making it possible for devicesconstructed in accord with the present invention and utilizing such hardferrous alloy electrodes to operate at greatly increased voltageswithout the danger of spurious breakdown or, in the alternative, tolocate the arc electrodes much closer together for a given holdoffvoltage. This characteristic seems to be associated with hardness of theelectrode and therefore is to be found in other hard ferrous metalelectrodes as well.

In general, in addition to the steels set forth herein, many othersteels containing nickel, chromium and other similar transition metals,are uniquely adapted to possess the highly desirable temperature and agehardening characteristics which optimize the use of ferrous arcelectrode assemblies in accord with the present invention.

Devices constructed in accord with the invention have been operatedrepeatedly to hold off 100,000 volts in open circuit position. In closedcircuit position, they have routinely successfully carried 33,000amperes peak current. This current has been interrupted successfully bycausing arc to be struck which exhibits a 50 V are drop and which hasbeen extinguished at a first current zero with no noticeable deleteriouseffects to the arc-electrodes and the applied voltage held off withoutrestrike.

FIG. 4 of the drawings illustrates a triggerable vacuum gap device 30 inaccord with the present invention which is a modification of the deviceof FIG. 1. In FIG. 4, like numerals have been utilized to identify likeparts thereto. Triggerable vacuum arc device 30 includes envelope 14 andits constituent parts, as illustrated in FIG. 1. Additionally, a triggerelectrode assembly 31 is electrically connected at one terminal thereofto lower endplate l7 and includes a metallic plated and scored insulator32, a trigger anode 33, and a trigger anode connector 34. Triggerassembly 31 may conveniently be any of the trigger assemblies set forthin Lafferty US. Pat. Nos. 3,394,281, 3,465,192 and 3,465,205, or thefunctional equivalents thereof. In operation, the trigger is operative,with the electrode assembly 12 momentarily negatively biased, to receivea positive pulse to trigger anode lead 34, causing the establishment ofa trigger arc between trigger anode 33 and the surface of arc electrodeplate 17 to cause the injection of an electron ion plasma into thevolume of envelope l4 and the breakdown of the respective interelectrodegaps 21 to cause the main voltage applied between terminals 28 and 29 toestablish parallel arcs, the aggregate of which may be in the hundredsof kiloamps range between the individual arc electrode rods 16 and 18 ofarc electrode assemblies 11 and 12. In operation, normally triggerablevacuum arc device 30 may be connected across a circuit constituent as,for example, a capacitor to be protected. Upon the occurrence of anoverload, a signal applied to trigger anode 33 to cause theinstantaneous breakdown thereof, short-circuiting the line therethroughwhile the fault which caused the transient is remedied or while thetransient, as for example, lightning-induced transient, passes. Upon theoccurrence of the next value of current zero, conduction species, whichare the metallic particles ejected from the arc electrode assemblies,condense on the shield and the electrodes. This occurs very rapidly inview of the rapid dielectric strength recovery characteristic of theferrous arc electrode materials in accord with the present invention, asdescribed hereinbefore. The arc is then not restruck upon the nexthalf-cycle of the alternating voltage and the device remains in thenonconducting, equilibrium state until the next trigger operationoccurs.

FIG. of the drawings illustrates a vacuum switch constructed in accordwith the present invention. Basically, the switch 40 of FIG. 5, whereinlike numerals are used to identify like parts to those of the device ofFIG. 1, comprises an array of a pair of arc electrode assemblies 11, 12,constructed of hard, ductile ferrous materials, as describedhereinbefore, but also containing a pair of butt-type electricalcontacts 41, 42 which constitute means for providing an electron-ionplasma within the arcing chamber of envelope 40. Normally, this devicemay be utilized in a closed circuit condition and the starter electrodes41 and 42, which are respectively mounted upon fixed supportrod 43 andmovable support rod 44, which is connected through bellows means 45 toan actuating arm (not shown), carry the steady-state current.

As is mentioned hereinbefore, the ferrous materials of the presentinvention are not adapted to carry a steady-state high circuit in vacuumarc devices in accord with the present invention. In such anarrangement, therefore, the central portions 46 and 47 of support rods43 and 44, respectively, are normally fabricated from copper, silver,alloy or equivalent conductor which exhibits a low resistivity so as notto cause excessive heating and other deleterious effects. Such cuprousand equivalent low resistivity materials are ideally not suited forexposure to the operation of the device under arcing conditions,however. Should this occur, the vapor pressure of the copper or cuprousalloy could cause the emission of copper or other vapor which maydeposit upon the surface of the ferrous arc electrode and shield membersof the device so as to degrade the dielectric strength and the recoverycharacteristics of the device. Accordingly, in such device a pair ofcladding members 48 and 49, which may for example be cylindrical'innature, are press-fitted, or otherwise caused to enclose totally anysurface of support members 43 and 44 that is within envelope 14, so thatthe only materials exposed to the operation of the highcurrent arcduring operation are ferrous materials.

In operation, the device 40 of FIG. 5 is in a normally conductivecondition with current flowing through the support members 43 and 44 andacross contacts 41 and 42 which are ferrous, as is describedhereinbefore, but of minimal thickness so as not to cause undue heating.Upon the occurrence of a fault or other reason for interrupting the flowof current within the circuit, a mechanical system (not shown) may beactuated to cause the movable support member 44 to be urged outwardly,as indicated by arrow 50, to cause the establishment of aninterelectrode gap between now separated starter electrodes 41 and 42.When the distance between starter electrodes 41 and 42 exceeds thedimension of interelectrode gaps 21 between respective rodlike members16, 18, of arc electrode assemblies 11 and 12, particularly in view ofthe normal characteristic of the butt-type electrode to impel an arcoutwardly, the arc is transferred to the parallel rod array and isdistributed over the parallel paths 21 of FIG. 2 between oppositelypoled parallel rods of arc electrode assemblies 11 and 12. Thiscondition exists until the occurrence of a current zero, as is describedhereinbefore, at which time the arc is extinguished.

Under certain circumstances, the delay caused by the mechanicalmanipulation of starter electrodes 41 and 42 and the support rodstherefor may not be fast enough for the operation of the device. Thus,with the device in the normally open position, a triggerable vacuumswitch may function by the addition of the trigger electrode structureas illustrated in the triggerable vacuum gap device 30 of FIG. 4 whichmay be actuated instantaneously upon the occurrence of a fault orovervoltage to change the device to the closed circuit condition andcause the fault current to be distributed across the rod array ofassemblies 11, 12 even before the approaching starter electrodes 41 and42 have an oportunity to close and carry the fault current.

As is readily apparent from the foregoing, the invention disclosedherein is applicable to a variety of devices, all of which arecharacterized as vacuum arc devices, but which may be switches,reclosers, gaps, triggered vacuum gaps, or the like. Accordingly, it iswithin the true spirit and scope of the invention that such applicationsof the principles of this invention to similar devices as fall withinthe purview of one skilled in the art shall be considered a practice ofthe invention.

While the invention has been disclosed hereinbefore with respect tocertain specific embodiments and specific and illustrative examples ofthe invention, many modifications and changes will readily occur tothose skilled in the art. Accordingly, I intend by the appended claimsto cover all such modifications and changes as fall within the truespirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A vacuum arc device adapted tp carry high currents at high voltagesand comprising:

a. an hermetically-sealed envelope evacuated to a pressure of 10 torr,or less;

b. a first primary arc electrode assembly disposed within said envelopeand including a first plurality of spaced, substantially parallel,rod-like electrode members having smooth arcing surfaces extendingsubstantially'normal to a first common base member;

c. a second primary arc electrode assembly within said envelope andincluding a second plurality of spaced, substantially parallel, rod-likeelectrode members having smooth arcing surfaces extending substantiallynormal to a second common base 'member and interleaved in alternatingsequence between the spaced electrode members of said first arcelectrode assembly;

d. said first and second spaced electrode members being positioned so asto form a ring-like array of electrode members within said envelope,said members alternating in polarity about said ring;

e. said electrode assemblies comprising ferrous material having ahardness as evidenced by a tensile strength of at least 100,000 psi anda ductility as evidenced by at least a percent elongation of a standardtwo inch long sample of standard ductility test cross section and havinga substantial freedom of sorbed gases and gas-forming impurities thereinso as to withstand arcing current densities of approximately 200amperes/cm for a half-cycle of power-alternating voltage without theemission of any substantial quantityof gaseous material inconsistentwith continued maintenance of said low pressure after having been arcedthereby;

f. shield means surrounding said are electrode members to confine arcingspecie to the interior thereof; and

g. means connecting said arc electrode assemblies in circuit with anelectric load.

2. The device of claim 1 wherein said first electrode assembly includesan upper base member and a plurality of downwardly-depending smoothsurface, rod-like electrode members and said second electrode assemblyincludes a base member and aplurality of upwardlydepending smoothsurface, rod-like electrode members.

3. The device of claim 2 wherein each of said ferrous electrodeassemblies is a vacuum-melted steel.

4. The device of.claim 3 wherein said ferrous electrode assemblies arefabricated from hardened steel having a Rockwell C hardness in excess of30, a yield strength in excess of approximately 150,000 psi, and aductility corresponding to an elongation of at least approximatelypercent of a 2 inch long standard cross section test sample.

5. The device of claim 4 wherein said ferrous material is atransformation induced plasticity steel.

6. The device of claim 4 wherein said ferrous metal is a maraging steel.

7. The device of claim 4 wherein said ferrous material is a carbon alloysteel having from 0.2 to 0.6 weight percent carbon therein.

8. The device of claim 4 wherein said ferrous assemblies are fabricatedof a temperature annealing steel which increases in ductility duringvacuum bakeout cycles used to fabricate vacuum arc devices of the orderof 500 600 C.

9. The device of claim 2 wherein the device further includes means forestablishing an electric arc between said arc electrode assemblies byestablishing an electron-ion plasma therebetween.

10. The device of claim 9 wherein said device is a triggerable vacuumgap device and the means for supplying an electron-ion plasma therein isa trigger electrode assembly.

1 l. The device of claim 9 wherein the device is a vacuum switch and themeans for supplying an electronion plasma therein is a starter electrodeassembly adapted to establish a starter arc discharge therein.

12. The device of claim 9 wherein said starter electrode assemblyconstitutes a pair of arc electrodes located at the approximatelongitudinal axis of said array.

13. The device of claim 12 wherein said starter electrodes are comprisedof the same materials as said primary arc electrode assemblies.

14. The device of claim 12 wherein said starter electrodes aresupplemented by a trigger electrode assembly to facilitate a reclosermode of operation.

15. The device of claim 12 wherein said starter electrodes are supportedupon a pair of arc support members, the exterior surfaces of whichconsist essentially of ferrous material.

16. The device of claim 1 wherein said ferrous assemblies are fabricatedof age-hardened steel which increases in hardness and yield strengthduring vacuum bakeout cycles used to fabricate vacuum are devices.

17. The device of claim 16 wherein saidbakeout temperatures are of theorder of 900l 200F and are utilized for periods of from 5 24 hours.

18. The device of claim 16 wherein said hardness after vacuum bakeout isapproximately at least 40 Rockwell C and is accompanied by a yieldstrength of at least approximately 150,000 psi.

19. The device of claim 1 wherein said ferrous metal is precipitationhardened.

1. A vacuum arc device adapted tp carry high currents at high voltagesand comprising: a. an hermetically-sealed envelope evacuated to apreSsure of 10 5 torr, or less; b. a first primary arc electrodeassembly disposed within said envelope and including a first pluralityof spaced, substantially parallel, rod-like electrode members havingsmooth arcing surfaces extending substantially normal to a first commonbase member; c. a second primary arc electrode assembly within saidenvelope and including a second plurality of spaced, substantiallyparallel, rod-like electrode members having smooth arcing surfacesextending substantially normal to a second common base member andinterleaved in alternating sequence between the spaced electrode membersof said first arc electrode assembly; d. said first and second spacedelectrode members being positioned so as to form a ring-like array ofelectrode members within said envelope, said members alternating inpolarity about said ring; e. said electrode assemblies comprisingferrous material having a hardness as evidenced by a tensile strength ofat least 100,000 psi and a ductility as evidenced by at least a 5percent elongation of a standard two inch long sample of standardductility test cross section and having a substantial freedom of sorbedgases and gas-forming impurities therein so as to withstand arcingcurrent densities of approximately 200 amperes/cm2 for a half-cycle ofpower-alternating voltage without the emission of any substantialquantity of gaseous material inconsistent with continued maintenance ofsaid low pressure after having been arced thereby; f. shield meanssurrounding said arc electrode members to confine arcing specie to theinterior thereof; and g. means connecting said arc electrode assembliesin circuit with an electric load.
 2. The device of claim 1 wherein saidfirst electrode assembly includes an upper base member and a pluralityof downwardly-depending smooth surface, rod-like electrode members andsaid second electrode assembly includes a base member and a plurality ofupwardly-depending smooth surface, rod-like electrode members.
 3. Thedevice of claim 2 wherein each of said ferrous electrode assemblies is avacuum-melted steel.
 4. The device of claim 3 wherein said ferrouselectrode assemblies are fabricated from hardened steel having aRockwell C hardness in excess of 30, a yield strength in excess ofapproximately 150,000 psi, and a ductility corresponding to anelongation of at least approximately 10 percent of a 2 inch longstandard cross section test sample.
 5. The device of claim 4 whereinsaid ferrous material is a transformation induced plasticity steel. 6.The device of claim 4 wherein said ferrous metal is a maraging steel. 7.The device of claim 4 wherein said ferrous material is a carbon alloysteel having from 0.2 to 0.6 weight percent carbon therein.
 8. Thedevice of claim 4 wherein said ferrous assemblies are fabricated of atemperature annealing steel which increases in ductility during vacuumbakeout cycles used to fabricate vacuum arc devices of the order of500* - 600* C.
 9. The device of claim 2 wherein the device furtherincludes means for establishing an electric arc between said arcelectrode assemblies by establishing an electron-ion plasmatherebetween.
 10. The device of claim 9 wherein said device is atriggerable vacuum gap device and the means for supplying anelectron-ion plasma therein is a trigger electrode assembly.
 11. Thedevice of claim 9 wherein the device is a vacuum switch and the meansfor supplying an electron-ion plasma therein is a starter electrodeassembly adapted to establish a starter arc discharge therein.
 12. Thedevice of claim 9 wherein said starter electrode assembly constitutes apair of arc electrodes located at the approximate longitudinal axis ofsaid array.
 13. The device of claim 12 wherein said starter electrodesare comprised of the same materials as said primary arc electrodeassemblies.
 14. The device of claim 12 wherein said starter electrodesare supplemented by a trigger electrode assembly to facilitate arecloser mode of operation.
 15. The device of claim 12 wherein saidstarter electrodes are supported upon a pair of arc support members, theexterior surfaces of which consist essentially of ferrous material. 16.The device of claim 1 wherein said ferrous assemblies are fabricated ofage-hardened steel which increases in hardness and yield strength duringvacuum bakeout cycles used to fabricate vacuum arc devices.
 17. Thedevice of claim 16 wherein said bakeout temperatures are of the order of900*-1200*F and are utilized for periods of from 5 - 24 hours.
 18. Thedevice of claim 16 wherein said hardness after vacuum bakeout isapproximately at least 40 Rockwell C and is accompanied by a yieldstrength of at least approximately 150,000 psi.
 19. The device of claim1 wherein said ferrous metal is precipitation hardened.